Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$71.64	4.382%	$74.7793	$74.78	$74.80	$74.80
Purchase #2	$207.58	13.648%	$235.9105	$235.91	$235.90	$235.90
Purchase #3	$163.98	6.459%	$174.5715	$174.57	$174.55	$174.60
Purchase #4	$89.32	11.215%	$99.3372	$99.34	$99.35	$99.30
Purchase #5	$40.57	4.143%	$42.2508	$42.25	$42.25	$42.30
Purchase #6	$109.55	8.772%	$119.1597	$119.16	$119.15	$119.20
Purchase #7	$222.70	12.160%	$249.7803	$249.78	$249.80	$249.80
7 purchase totals =	$905.34		$995.7893	$995.79	$995.80	$995.90